ISDN is expected to be a rapidly expanding branch in the data communicating field as it allows the possibility of high-rate communications in the near future, particularly for sending voice, data etc.
FIG. 1 shows an example of ISDN connections. A calling terminal adapter 20 allows the connection of a Data Terminating Equipment (DTE) 10 to I.S.D.N. telecommunication network 50.
In the considered example, a calling terminal adapter 20, assumed to be a telecommunication equipment located within the United States of America, is designed to be connected to the well-known AT&T ACCUNET network. With this assumption, Terminal adapter 20 is capable of handling 56 Kbps links and utilizes the well known I.S.D.N numbering plan. A second Terminal Adapter 60 is also connected to the network 50 and is assumed to be an ISDN terminal adapter capable of handling 64 Kbps. At last, a third terminal adapter 30 allows the connection of a DTE 40 to the network.
Therefore, it appears that when one call is received by one terminal Adapter, e.g. adapter 30, the latter needs to recognize the rate and accordingly adapts its own speed to that used by the calling party. Indeed, assuming that adapter 20 is the calling one, the called adapter 30 needs to be adapted to a 56 Kbps rate. Conversely, in the case where the calling adapter is adapter 60, the called adapter needs to switch its operating speed to a rate of 64 Kbps.
In the prior art, the switching between the two operating rates was performed manually by the user prior to the call or a user was compelled to buy a series of two distinctive equipments, each one being dedicated to one particular speed.
Therefore, a need has appeared in the telecommunication field for an ISDN equipment which is capable of automatically recognizing and adapting its own speed to either 56 Kbps and 64 Kbps.